Thank you for your answer, there's a lot of good information there. I don't think I actually have chapped lips, because they are not peeling. I do think I am dehydrated though, so I need to drink more water.
I don't smoke or wear dentures, but I do eat a lot of sugary foods and drink Coke every day (about 1 a day).
I think I can rule out a gum or mouth injury, because I can't think of anything like that happening.
I will have to check into those other conditions you listed to see if one of those could be a possibility, because I honestly do not know.
Of all of the things you listed, after looking up other symptoms related to those conditions, Vitamin B2 and B12 deficiencys sound like the most probable, particularly B2. I have many of the symptoms associated with this deficiency. Insomnia, eyes overly sensitive to lights and tired easily and I take 50mcg of Synthroid daily.
I was told by one doctor that I take as much as someone without a thyroid gland would have to take. However, the last few times my thyroid levels were tested, they came up okay.